Automatic lifting tongs

ABSTRACT

Lifting tongs have a pair of primary arms forming a pair of jaws for engagement with a workpiece. A latch mechanism interlocks the two arms so that the tongs can be opened and closed automatically by successive movements opening the jaws. Following a first movement opening the jaws, the latch mechanism is engaged to hold the jaws open; the latch mechanism is disengaged by a subsequent movement opening the jaws whereupon it releases the arms to allow the jaws to close. The latch mechanism includes a pivoted latch member mounted on one arm, which latch member is movable between two equilibrium positions to define the engaged and disengaged positions of the latch mechanism.

United States Paten J ohnstone et al.

[ AUTOMATIC LIFTING TONGS [72] Inventors: Crichton Lockhart Johnstone,135 Avon Street, Motherwell; John Woodhouse Paton, 3 Clark Street,Newmains, both of Scotland [22] Filed: Nov. 30, 1970 [21] Appl. No.:93,698

[30] Foreign Application Priority Data Dec. 2, 1969 Great Britain..58,899/69 [52] US. CLI ..294/ll0 R, 294/119 [51] Int. Cl. ..B66c 1/44[58] Field of Search ..294/109, 110, 119, H8, 106, 294/1 16; 292/338,DIG. 4

[56] References Cited UNITED STATES PATENTS 2,337,177 12/1943 Breslav..294 /l 10 [451 Oct. 10,1972

Primary Examiner-Even C. Blunk Assistant Examiner.lohnny D. CherryAttorney-Holcombe, Wetherill & Brisebois [57] ABSTRACT Lifting tongshave a pair of primary arms forming a pair of jaws for engagement with aworkpiece. A latch mechanism interlocks the two arms so that the tongscan be opened and closed automatically by successive movements openingthe jaws. Following a first movement opening the jaws, the latchmechanism is engaged to hold the jaws open; the latch mechanism isdisengaged by a subsequent movement opening the jaws whereupon itreleases the arms to allow the jaws to close. The latch mechanismincludes a pivoted latch member mounted on one arm, which latch memberis movable between two equilibrium positions to define the engaged anddisengaged positions of the latch mechanism.

' 10 Claims, 5 Drawing Figures PATENTEnw'wwn 3.697.118

SHEET 1 [IF 3 PATENTED 3.697.118

' sum-2 0F 3 AUTOMATIC LIFIING TONGS This invention relates to liftingtongs. The invention is particularly applicable to lifting tongs whichare intended to lift relatively heavy workpieces, for example, ingotssuch as are handled in Steel Works, and which must for safety reasons beremotely controlled.

Lifting tongs of this kind must be capable of retaining in an openposition the jaws which engage with the workpiece and provide quick andeasy closure of the jaws onto the workpiece after they have been placedin the correct position with respect to the workpiece. The tongs must inaddition provide for quick and easy opening of the jaws to release theworkpiece when this has been hoisted into position and subsequentlyagain to retain the jaws open for a further sequence of operatrons.

One method of meeting these requirements has been to operate the jaws bymeans of a mechanism known as dogging gear which is actuated by a cableindependently of the cable by which the tongs are hoisted. This system,while satisfactory and reliable under arduous conditions such as areencountered in an ingot soaking pit, requires the hoisting crane to beprovided not only with an additional and independent operating mechanismfor the gear, but also with an additional set of manual controls whichrequire operation in an already complex console.

Attempts have been made to overcome the cost and operational difficultyof dogging, by providing tongs with means which automatically lock andunlock the jaws in response to the upward thrust against the arms of thetongs themselves.

A number of such tongs in which the means generally comprise a latchingmechanism have been proposed; however, these have been found susceptibleto impact, for example, by surging against the sides of the soaking pitand have been found unsatisfactory either in this respect or in respectof cost.

According to one aspect of the present invention, there is providedlifting tongs comprising a pair of primary arms pivotally connected toone another to form a pair of jaws for engagement with a workpiece, anda latch mechanism connected to the primary arms, the latch mechanismincluding a pivotally mounted latch member which adopts a first positionwhere it prevents closure of the jaws, and a second position where itallows closure of the jaws, in response to successive opening movementsof the jaws.

Preferably, the latch member is pivotally mounted upon one arm of thetongs and is adapted to engage with a cooperating projection provided onthe other arm.

In one embodiment the latch member is pivotally mounted on one arm andhas an opening to receive a cooperating projection on the other arm, theopening being so shaped that the projection is moved around at leastpart of the periphery of the opening by the said successive openingmovements.

Preferably, the opening has a region adapted to restrain the projectionagainst movement corresponding to closure of the jaws, the periphery mayinclude a re-entrant portion for engaging the projection to restrain itsmovement with respect to the latch member in the direction correspondingto closure of the jaws. Alternatively, however, such selective restraintagainst movement may be provided by an auxiliary latch member which isdisplaced by the projection on one part of its movement corresponding toopening of the jaws and which subsequently acts to restrain theprojection against movement corresponding to closure of the aws.

Preferably, the said first and second positions of the pivoted latchmember are two equilibrium positions. In one such embodiment the latchmember reaches each equilibrium position during relative movementbetween itself and the projection on the said other arm of the tongscorresponding to closure of the jaws, and is displaceable from theequilibrium position only by relative movement corresponding to openingof the jaws. In this case the projection in one equilibrium position isurged against that region of the opening which contains the re-entrantportion or auxiliary latch, to permit engagement to occur. In responseto an opening of the jaws the latch member subsequently is moved intothe second equilibrium position in which the projection is urged againstthe opposed region of the opening preventing re-engagement with there-entrant portion as the cycle is continued.

Preferably the latch member is moved between the equilibrium positionsby cam reactions between the projection and the profile of the opening.The equilibrium positions may be maintained solely by gravity or may beassisted by an over-center spring arrangement suitably incorporated intothe latch mechanism.

The projection may incorporate a roller effective to reduce thefrictional drag produced by movement relative to the periphery.

Preferably, the arms of the tongs are in the form of spaced platessecured together by bridges; in this case the latch mechanism isdisposed between the plates to provide protection particularly againstmechanical impact. The latch mechanism may be secured between any regionof any pair of arms of the tongs which cooperate to produce opening andclosure of the jaws.

One embodiment of the invention will now be particularly described byway of example, with reference to the accompanying drawings in which:

FIG. 1 is a perspective side view of the tongs according to theinvention,

FIG. 2 is a sectional side view which shows the tongs fully extendedwith the jaws closed in engagement with a workpiece,

FIG. 3 is a sectional side view of the tongs shown in FIG. 1 and in oneoperational position, and

FIG. 4 is a fragmentary view of the latch mechanism shown in FIG. 2 butin a second operational position.

FIG. 5 is a view of an alternative latch mechanism shown in the sameposition as the latch mechanism of FIG. 4.

Referring to the drawings and in particular to FIG. 1, the lifting tongscomprise two primary arms 2 and 4 each in the form of two identicalspaced plates secured together by bridges S in a manner well known inthe art. The arms are pivoted to one another at a point substantiallybetween their normally upper ends and their lower ends which constitutethe jaws for engagement with the workpiece. To assist the jaws to grip,in this case the sides of an ingot being lowered into and raised from asoaking pit, the jaws are provided with tapered tips 8 effective to biteinto the ingot sides and lessen the risk of accidental release duringhoisting.

Two secondary arms 9 and 10 have their lower ends secured by way ofpivots 12 and 14 to arms 2 and 4 and have both their upper ends pivotedto a yoke 16 by which the tongs can be secured to the hook or sling of asuitable lifting crane. In use, hoisting produces lifting of the tongsas a whole while causing the jaws 8 to close upon and grip a workpiecelocated between them. I

A latch mechanism is provided to automatically maintain the jaws in theopen position to receive a workpiece and subsequently automatically torelease the jaws for closure.

The latch mechanism comprises a member 20 secured to arm 4 by way of apivot 21 and having a profiled opening 22 terminating at its upper endin a substantially linear guide portion 24, which although shownopen-ended may be closed off. A projection 26, which may be in the formof a fixed spigot or a roller mounted upon primary arm 2 is arranged tobe received within the opening 22 and to slidably move cyclically aroundits periphery.

With the jaws in the closed position as shown in FIG. 2, either engaginga workpiece or otherwise, the projection 26 will lie at the upper end ofthe guide portion 24. The length of the guide portion 24 is selected tobe sutficient to accommodate the excursion of the spigot 26 for anyparticular degree of closure which is limited by an abutment 36 providedon arm 4 and arranged for engagement with arm 2.

As the tongs are lowered onto a supporting surface, upward thrust,applied directly or indirectly to the arms 2 and 4 by way of aworkpiece, produces opening movement of the jaws and causes theprojection 26 to move down the guide portion 24 until it reaches thelower guide limit defined by elbow 30.

The center of gravity of the member 20 is selected such that at thisstage it is in a first equilibrium position whereby further downwardmovement of the projection relatively to the opening 22 automaticallyallows the member to tilt for engagement of the projection with are-entrant portion 32 of the opening periphery (see FIG. 3). The shapeof the re-entrant portion is effective to prevent disengagement whilethe weight of the tongs is supported solely by the yoke 16 and preventsclosure of the jaws 8.

A successive and independent upward thrust against the arms 2 and 4 byre-lowering of the tongs against the supporting surface reopens the jawsto release the workpiece, if originally held. Reopening continues thecyclic movement of the spigot around the periphery of the opening 22 tothe lowermost point 34 (see FIG. 4); further closure when this point isreached being prevented by an additional abutment 28.

At this stage the member 20 is moved into its second equilibriumposition by reaction between the projection 26 and the profile of theopening 22 so that with further closure of the jaws produced by liftingof the tongs, the portion 40 of the channel profile is urged against theprojection 26. This enables the projection to continue and complete itscycle to the top of the guide portion 24 without re-engagement withportion 32.

The tongs are now ready for a further cycle of operation in response tosuccessive forces applied to arms 2 and 4.

In use, the crane which hoists the automatic lifting tongs of theinvention is controlled from a cabin often at considerable height abovethe ground level. To enable the operator to obtain a clear indication ofthe extent to which the jaws have opened, particularly to see if theyhave opened sufficiently to positively operate the latch mechanism, asuitable indicator may be provided on the tongs. This may be of any typewell known in the art, for example a pointer arm, which conveniently isconstituted by an extension of the linear guide portion 24 of the latchmember 20.

It will be appreciated that while a re-entrant portion 32 has beendescribed as automatically preventing closure, this could otherwise beachieved, for example, by a further pivoted latch.

It will also be appreciated that while the tongs have been described asprovided with jaws in the form of tapered tips, any form of jaw adaptedto engage with different types of workpieces, for example, barrels,planks, sacks, not necessarily connected with the steel industry, may beused.

For the sake of safety the crane hook is fitted with an attachment or isadapted, as is well known, to prevent release of the tongs if these areexcessively lowered.

FIG. 5 shows an alternative latch mechanism in the same position as thelatch mechanism of FIG. 4. The alternative latch operates onsubstantially the same principle except that an auxiliary latch 50 isprovided in place of the re-entrant portion 32. The latch 50 is pivotedat 51 and biased in a counter clockwise direction by a spring 52 againsta stop 53. The pivoted latch member 20 is moved by cam reaction with theprojection 26 in exactly the same way as the preceding embodiment but aspring 54 is provided in an overcenter arrangement to assist in biasingthe latch member 20 to its equilibrium positions. The spring 54 iscompressed between a stop 55 mounted on the arm 4 and a stop 56 formedon the far end of an opening 57 in the latch member 20, within which thespring 54 is located. The position of the over-center spring in theother equilibrium position is shown at 58 in broken outline.

We claim:

1. Lifting tongs comprising:

a pair of primary arms pivotally connected to one another and defining apair of jaws for engagement with a workpiece; and

a latch mechanism mounted on said primary arms, said latch mechanismincluding a latch member having an internally profiled opening pivotallymounted on one of said arms and a projection rigidly mounted on theother of said arms, said projection being retained in and co-operatingwith said opening;

the internal profile of said opening so shaped and the mounting pointson said primary arms of said projection and latch member being sopositioned that, in response to successive opening movements of saidjaws, said projection moves within said opening around the periphery ofsaid opening and pivots said latch member between a first positionpreventing closure of said jaws and a second position allowing closureof said jaws.

2. The lifting tongs of claim 1, wherein said periphery of said openinghas a region integral with said latch member adapted to restrain saidprojection against movement corresponding to closure of said jaws.

3. The lifting tongs of claim 2, wherein said region includes are-entrant portion for engaging said projection to restrain its movementwith respect to said latch member in the direction corresponding toclosure of said jaws.

4. The lifting tongs of claim 3, wherein said region includes anauxiliary latch member displaceable by said projection on the part ofits movement corresponding to opening of said jaws and whichsubsequently acts to restrain said projection against movementcorresponding to closure of said jaws.

5. The lifting tongs of claim 1, wherein said first and second positionsof said pivoted latch member are equilibrium positions.

6. The lifting tongs of claim 5 wherein said latch member reaches eachequilibrium position during movement of said primary arms correspondingto closure of said jaws, said latch member being placeable from saidequilibrium position only by movement of said primary arms correspondingto opening of said aws.

7. The lifting tongs of claim 5 wherein said latch member is movedbetween said equilibrium positions by cam reactions between saidprojection and said internal profile of said opening.

8. The lifting tongs of claim 5 wherein said equilibrium positions ofsaid latch member are maintained by a spring in an over-centerarrangement.

9.The lifting tongs of claim 5 wherein said equilibrium positions ofsaid latch member are maintained by gravity, said latch member beingmounted with its pivot below its center of gravity.

10. The lifting tongs of claim 1, wherein said arms of said tongs are inthe form of space plates having bridges securing said spaced platestogether, said latch mechanism being disposed between said spacedplates.

UNITED STATES PATENT OFFICE CERTIFICATE F CQ'RECTION Patent 3,697,118Dated October 10 1972 CRICHTON LOCKHART JOHNSTO NE and I JOHN WOODHOUSEPATON It is certified that error appears in the above-identified patentY and that said Letters Patent are hereby corrected as shown below:

[73] Assignee: The British Steel Corporation, London, England Signed andsealed this 22nd day of May 1973.

(SEAL) Attest:

Y EDWARD M.FLET CHER,JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents F ORM PO-l 050 (10-69) USCOMM-DC 6Q376-P69 kU.S. GOVERNMENT PRINTING OFFICE: 1969 Q3$6-3S4

1. Lifting tongs comprising: a pair of primary arms pivotally connectedto one another and defining a pair of jaws for engagement with aworkpiece; and a latch mechanism mounted on said primary arms, saidlatch mechanism including a latch member having an internally profiledopening pivotally mounted on one of said arms and a projection rigidlymounted on the other of said arms, said projection being retained in andco-operating with said opening; the internal profile of said opening soshaped and the mounting points on said primary arms of said projectionand latch member being so positioned that, in response to successiveopening movements of said jaws, said projection moves within saidopening around the periphery of said opening and pivots said latchmember between a first position preventing closure of said jaws and asecond position allowing closure of said jaws.
 2. The lifting tongs ofclaim 1, wherein said periphery of said opening has a region integralwith said latch member adapted to restrain said projection againstmovement corresponding to closure of said jaws.
 3. The lifting tongs ofclaim 2, wherein said region includes a re-entrant portion for engagingsaid projection to restrain its movement with respect to said latchmember in the direction corresponding to closure of said jaws.
 4. Thelifting tongs of claim 3, wherein said region includes an auxiliarylatch member displaceable by said projection on the part of its movementcorresponding to opening of said jaws and which subsequently acts torestrain said projection against movement corresponding to closure ofsaid jaws.
 5. The lifting tongs of claim 1, wherein said first andsecond positions of said pivoted latch member are equilibrium positions.6. The lifting tongs of claim 5 wherein said latch member reaches eachequilibrium position during movement of said primary arms correspondingto closure of said jaws, said latch member being placeable from saidequilibrium position only by movement of said primary arms correspondingto opening of said jaws.
 7. The lifting tongs of claim 5 wherein saidlatch member is moved between said equilibrium positions by camreactions between said projection and said internal profile of saidopening.
 8. The lifting tongs of claim 5 wherein said equilibriumpositions of said latch member are maintained by a spring in anover-center arrangement.
 9. The lifting tongs of claim 5 wherein saidequilibrium positions of said latch member are maintained by gravity,said latch member being mounted with its pivot below its center ofgravity.
 10. The lifting tongs of claim 1, wherein said arms of saidtongs are in the form of space plates having bridges securing saidspaced plates together, said latch mechanism being disposed between saidspaced plates.